This invention relates in general to filters and more specifically to flexible filters for percutaneous insertion and placement within a fluid passageway of a living body.
Pulmonary embolism is a disease occurring at a frequency of over 600,000 symptomatic cases per year in the United States. Pulmonary embolism is the sudden obstruction of a blood vessel by blood emboli, the emboli typically formed in the veins of the pelvis and lower extremities of a living body. Because migration of the blood emboli to the pulmonary artery can interrupt the oxygenization process in the lungs, the disease has a high mortality rate with over 200,000 deaths each year in the United States. Vena cava filters, therefore, have been developed as one method for preventing pulmonary embolism.
Historically, vena cava filters have been implanted surgically requiring ligation of the inferior vena cava. Although initially effective against pulmonary embolism, caval ligation carries a very high operative mortality, up to 50% in some cases. This high mortality rate stimulated development of devices that could be placed within the caval lumen which do not require general anesthesia and surgery. One device by Mobin-Uddin, U.S. Pat. No. 3,540,431, describes a filter comprising a skeletal body of struts expandable into a generally domed shaped configuration. Besides requiring a relatively large sized sheath for percutaneous insertion, this filter design can be susceptible to migration and to caval thrombosis. Other domed shaped filters include Gewertz, U.S. Pat. No. 4,969,891; Lebigot, U.S. Pat. No. 4,781,177; Metals, U.S. Pat. No. 4,688,553; and others by Mobin-Uddin, U.S. Pat. Nos. 4,643,184 and 4,727,873.
Other filters including a head with a plurality of legs extending therefrom are described by Herms et al., U.S. Pat. No. 4,817,600; Palmax, U.S. Pat. No. 4,793,348; and Kimmell, Jr., U.S. Pat. No. 3,952,747. These types of filters typically suffer problems including filter tilt, misplacement and migration.
In an attempt to overcome these problems, still other filters have been developed including Gianturco, U.S. Pat. No. 4,494,531. The Gianturco filter comprises a number of strands of shaped memory wire interconnected and tangled together to form a curly wire mesh, or "bird's nest". Another filter by Molgaard-Nielsen et al., U.S. Pat. No. 4,619,246, describes a collapsible filter basket comprising a plurality of resilient wires interconnected at their respective ends. Finally, Palestrant, U.S. Pat. No. 4,832,055, describes a mechanically locking blood clot filter, and Simon, U.S. Pat. No. 4,425,908, describes a blood clot filter comprising a material being pliable in its low temperature condition and being resiliently deformable and rigid in its high temperature condition.
While the above filters can be percutaneously inserted thus precluding surgery and its inherent mortality risks, there still exists a need for an improved percutaneously insertable filter providing greater ease of insertion, broader range of application and increased effectiveness. Such a filter should be insertable using a simple single step procedure employing transcatheter techniques. Such a device should also be collapsible into a small shape to pass through a small catheter system. Also desired is a device which is self-expanding, self-centering and includes multiple planes of filtration.